1. Field of the Invention
The present invention relates to a roll-stamper, which is employed for transferring a preformat pattern onto a surface of a substrate material in continuous production of a substrate of high-density information recording medium such as optical discs, optical cards, and the like. The present invention also relates to a molding apparatus employing the roll-stamper for forming substrates for an information recording medium.
2. Related Background Art
Substrates for a high-density optical information recording medium such as optical discs and optical cards can be produced by injection molding, compression molding, or extrusion molding.
The injection molding and the compression molding have disadvantages in that they require certain conditions of the pressure, the temperature of the molten resin and precision of the mold, etc. in order to achieve flatness and smoothness of the substrate, to prevent warp of the substrate, and to suppress the penetration of gas bubbles into the substrate. In addition, the molding machine is large-scaled and the production cost is high. Furthermore, the injection molding has difficulty in producing thin substrates (0.4 mm or less) such as optical cards. The compression molding is not highly productive since the sheets are treated one by one, post-treatment is troublesome, and much time is required for heating and cooling of the substrates.
On the contrary, the extrusion molding, which employs a compact molding machine, can form a substrate having a signal pattern such as preformat signal or tracking signal by extruding a resin sheet and pressing a roll-stamper onto the surface of the resin sheet without the above-mentioned inconvenience, and is suitable for mass production of the substrates. Accordingly, the substrates are generally produced by extrusion molding.
Conventional roll-stampers for forming substrates of information recording media are exemplified by those shown below:
(1) a sheet-type stamper having a preformed and engraved pattern on its surface is uniformly adhered on the peripheral face of a mirror roller (a roller having mirror-finished surface) with an adhesive; and
(2) As shown in FIG. 8, a sheet-shaped stamper (81) having a preformed and engraved pattern on its surface is fastened, with screws onto the peripheral face of a mirror roller 82.
The roll-stamper prepared by the above-mentioned technique (1) has a disadvantage that its life is extremely short because the adhesive fastening the stamper deteriorates by the heat of the extruded resin sheet or the roll-stamper itself and the stamper is liable to peel off from the mirror roller. Further, it involves another disadvantage that bubbles are liable to be formed in the adhesive and the protrusions caused by the bubbles are unnecessarily transferred onto the substrate, which interferes with the precise transfer of the pattern resulting in transferred pattern defects.
On the other hand, the roll-stamper prepared by the technique of (2) above involves the disadvantage that unevenness or distortion at the screw-fixed positions may cause defective pattern transfer, or exert an uneven pressure onto the resin sheet, resulting in, for example, birefraction of the polycarbonate used as a resin.
The present invention solves the above-described disadvantages of the prior art.